This invention relates to a heat-shrinkable composite packaging film having a core layer of saponified ethylene-vinyl acetate copolymer (hereinafter referred to as "EVOH") useful for packaging various meat products and the like.
It has long been the practice in the meat processing industry to enclose various meat products with a heat-shrinkable plastic film by vacuum packaging and then heating the resulting packs in hot water for sterilizing its contents while allowing the film to shrink by the heat. A variety of heat-shrinkable composite films having a layer of polyvinylidene chloride has been commercially available and widely used for this purpose. However, polyvinylidene based heat-shrinkable films have disadvantages in that they are often subjected to pinholes during packaging operations and transportation of packaged products resulting in contamination and spoilage of packaged contents. Polyvinylidene chloride based films have also been reported to generate carcinogenic dioxin upon combustion.
Heat-shrinkable two-ply films comprising a polyamide substrate layer and a heat-sealable plastic layer have also been used for the above-mentioned purpose, but their oxygen barrier properties are not high enough to ensure long term storage of various meat products packaged with these films.
Another type of heat-shrinkable composite films used for packaging meat products and the like comprises a core layer of EVOH sandwiched between a polyamide layer and a heat-sealable plastic layer. When these films are used to package meat or other products and soaked in hot water having a temperature above 90.degree. C. for sterilizing and shrinking, whitening and delamination of packaging films may often be experienced thereby rendering the content invisible and degrading the value of the packaged products.
Therefore, there is a strong demand for a heat-shrinkable composite packaging film which exhibits high oxygen barrier properties so as to enable storage of meat products and the like for a long period of time and which remains transparent without whitening and delamination after the sterilization and shrinking operation in hot water.